2 Answers
2

I'm not sure why installing from a usb stick is better. I think the safest way to install Ubuntu is with wubi. You don't have to mess around with the partition manager and it does not repartition your hard drive. It creates a "fake partition" which basically consists of a couple of files that reside in the ubuntu folder in windows. Its pretty amazing.

You should be fine. If you are re-installing over an old ubuntu system then you should be able to just select the same partitions and ubuntu will install right over the old one (no partitioning needed).